That was my initial thought but, if it's a typo, there are an awful lot of typos, since the rest of that paragraph and all of the next paragraph are talking about carbon 12-13 ratios. Whatever, it doesn't look as if whoever wrote it read what they had written very carefully before publishing it!I dont think you are dim. I think that final point should read "thus they have a lower carbon 14:12 ratio" a typo I think rather than a flawed point (or you being dim- it doesn't make any sense to me as it's written)
Kind Regards, John